The invention relates to a split electromechanical motor vehicle stabilizer having a locking device, and a method for roll stabilization of the vehicle which include a built in electromechanical actuator for bracing two stabilizer parts against one another.
It is known to divide a motor vehicle stabilizer into a first stabilizer part associated with the suspension of the left wheel on a vehicle axle, and a second stabilizer part associated with the suspension of the right wheel on this vehicle axle. When these stabilizer parts are mutually rotatable about their common longitudinal axis, a greatly increased roll support may be achieved compared to chassis having conventional stabilizers when the two stabilizer parts are rotated with respect to one another, as necessary, by suitable actuation provided by an actuator provided therebetween.
An electromechanical actuator that is suitable for this application comprises an electric motor and a mechanical gear unit. A stabilizer is thus obtained, the two stabilizer halves of which may be rotated with respect to one another in a targeted manner by the electromechanical actuator, thereby producing a desired stabilizer torque which then prevents roll of the vehicle bodywork.
German Patent Document DE 198 46 275 A1 describes such a split stabilizer having a built-in electric oscillating motor for roll control. By using the stabilizer parts designed as passive torsion springs, this split stabilizer is able to transmit pretensioning and thus a stabilization torque into the vehicle bodywork which counteracts a roll motion.
To allow pretensioning of the stabilizer parts for roll control, the oscillating motor must actively apply a defined torque, and thus be able to set a given angle of rotation between the two stabilizer parts. The magnitude of the torque to be applied must be selected in accordance with the magnitude of the roll motion.
If the roll control fails, for example due to an interruption in the power supply or malfunction of a system component, the actuator is no longer able to actively provide the necessary torque, which in the absence of further measures results in loss of activity of the two stabilizer parts, since the rotor and stator of the electric motor may be easily rotated with respect to one another.
To prevent this undesired rotation, the oscillating motor in German Patent Document DE 198 46 275 A1 has a brake which acts as a locking device between the two stabilizer parts in the event of a malfunction in the system. The stabilizer parts then act as a passive stabilizer which permits a roll angle that deviates from the roll angle in the actively stabilized state, but still allows travel to continue.
During cornering, however, if a transition from active roll control to passive roll stabilization occurs due to use of the brake, and the oscillating motor is locked, but the oscillating motor has pretensioned the stabilizer parts against one another, the vehicle continues traveling with the vehicle bodywork rotated about the longitudinal axis of the vehicle when cornering is completed.
The embodiments of the invention provide a split electromechanical motor vehicle stabilizer for roll stabilization and a method for roll stabilization for a motor vehicle in which these disadvantages do not occur during use of a locking device, and which in the event of failure of the roll control allows a mechanically functioning emergency operation of the stabilizer, which is employed as a function of the position on the input side over several rotations of the actuator, and which need only absorb the lower gear unit input load, not the high load on the output side.
According to an exemplary embodiment of the invention, a split motor vehicle stabilizer is provided for roll stabilization, having a built-in electromechanical actuator for bracing two stabilizer parts against one another, which includes at least an electric motor, a gear unit, and a locking device which can lock a housing for the actuator to a rotor in the electric motor, the housing being connected to one of the stabilizer parts, and a gear unit output shaft being connected to the other stabilizer part for the purpose of transmitting torque. The housing and the rotor can be locked relative to one another in only one position, for example the locking position, after the locking device is activated, and the locking position is the normal position for the two halves of the stabilizer in which they are not pretensioned against one another.
This embodiment provies the advantage that when the roll control shuts off or fails, the rotational motion of the two stabilizer parts relative to one another can be locked in only one position, which corresponds for example to the position on level ground with the wheels facing straight ahead. This advantageously ensures that at the end of a cornering maneuver, the vehicle does not have to continue travel with a vehicle bodywork rotated about the longitudinal axis of the vehicle if the roll control fails during the cornering. This is because, as a result of the pretensioning of the bodywork springs, the vehicle bodywork can resume a horizontal position before locking is initiated.
A fully mechanical, form-fit lock is still possible, however, as fail-safe protection in an exemplary gear unit which can be operated in oscillating mode with limitation of absolute revolutions, in order to allow the failure mode to be initiated in a defined horizontal position of the vehicle bodywork. A form-fit connection of the gear unit input shaft and the housing is advantageously established in the case of failure mode operation, the exemplary connection being made as a function of the position. The information concerning the location of the defined position of the mechanical locking is provided in this example by superimposing multiple, in this case two, mechanical position indicators.
In one exemplary preferred embodiment of the invention, the locking device includes a movable locking bar which is fixed to the housing, i.e., the rotor, so as to be displaceable in the axial position, and which by being moved into the locking position establishes a form-fit connection, having a locking effect in the circumferential direction, with at least one recess in the rotor, i.e., the housing. This advantageously ensures a particularly simple design of the locking device.
Alternatively, the exemplary locking device may also include a movable locking bar which is fixed to the housing or to the gear unit output shaft so as to be displaceable in the axial position, and which by being moved into the locking position establishes a form-fit connection, having a locking effect in the circumferential direction, with at least one recess in the gear unit output shaft or in the housing.
In one exemplary embodiment, the locking device may include an electromagnet which holds the locking bar against the pretensioning force of a spring in a nonlocking position, or in a locking position. As an alternative in the design of the locking device, a choice may be made as to whether the locking device will be used with or without the supply of current in the failure state.
In one preferred exemplary embodiment of the invention, the locking device includes a locking bar having at least three form-fit profiles: a first profile whose counter-profile is provided on the gear unit output shaft, a second profile whose counter-profile is provided on the rotor, and a third profile whose counter-profile is provided on the housing.
In one simple, particularly preferred exemplary embodiment of the invention, one of the three form-fit profiles is always engaged with its counter-profile for the purpose of fixing the locking bar in the circumferential direction and for axial guiding thereof. In addition, the other two form-fit profiles are engaged with their counter-profiles only when the locking device fixes the two stabilizer parts in the locking position.
One particularly advantageous exemplary method for roll control on a front and/or rear axle of a motor vehicle by using a split stabilizer, in which an electromechanical actuator compensates for roll motions of the vehicle bodywork with respect to the chassis by bracing the two stabilizer parts against one another in both rotational directions of the electromechanical actuator, in such a way that the vehicle bodywork maintains a substantially parallel horizontal plane. In this exemplary embodiment, following shutoff or in the event of failure of the electromechanical actuator, roll motions of the vehicle bodywork with respect to the chassis are influenced by the fact that the two stabilizer parts are connected to one another by a locking device in their normal position, namely the locking position. If an electromechanical actuator is provided on both the front and rear axles, the driving stability may be increased by locking only the stabilizer parts on the front axle, since undercontrol of the handling characteristics is achieved. In cases when this is the sole desired influence on the handling characteristics, the motor vehicle may also be equipped with split stabilizers in which only the actuator for the front axle is provided with a locking device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.